I have a question regarding the length of time it takes for alcohol to leave the system to a point where you are legal to drive.
Today a co-worker was coming to work and drove through a speed trap where he was stopped. The officer said he noticed an alcohol odour and gave him a breathalyzer where the reading was .055. The man said this had to be wrong and got a second reading at the station of .04. He affirms that he had been drinking the evening before (6-8 drinks depending on his opinion of what a drink size is) and that he was in bed at 10:30. He weighs about 200lbs. So there was at least 9 or 10 hours for the alcohol to metabolize and according to the internet on repeated sites all of the alcohol should have been gone.
Something does not make sense to me and I would appreciate your experienced thoughts.
In general, the average person eliminates about 0.015 or 15 mg% per hour. So, if your blood alcohol concentration (BAC) is .15 or 150 mg% when you stop drinking, you will take 10 hours before your body is able to rid itself of the alcohol that you have consumed.
If we look at your friend blowing .05 at 7:30 am for the sake of illustration, with cessation at 10:30 pm, there was a 9 hour interval. We'll give him an hour for all the alcohol that was in his stomach at 10:30 to be absorbed, so his body really spent about 8 hours metabolizing and eliminating alcohol without him adding to it. 8 times 15 mg% is 120 mg%. Add the 50 he blew and his peak blood alcohol was probably around 170 mg%.
For a 200 pound man to have a BAC of 170 mg% he would need to have consumed about 9 standard drinks. A standard drink is 12 oz. of regular beer, 5 oz. of wine or 1.5 oz. of hard liquor. So, if your friend was not measuring, his estimate is fairly close.
This has caught a few drivers off guard during my policing career. People tend to think that if they stop late in the evening they should be good to go by breakfast. However, as you have seen, if you have a high BAC when you stop it can take a long time before you fall below the 50 mg% IRP trigger level. It was not uncommon for me to be dealing with drivers whose BAC at time of driving was between 250 and 300 mg% when I worked in Fort St. John. For these people the entire following work day may have been spent over the limit!
Let's look at some real world scenarios?
If you've had a three pints of beer at the beach at 2PM and you weigh about 200 lbs. Would you be impaired? What would typically be your blood alchol level?
If you drive home at around 7PM, had protein before hand. Would you still be impaired? What would be a reasonable guess of your BAC level if the legal limit is now 0.05?
A pint is 16 ounces, which is 1.25 standard drinks. So your 3 pints is 3.75 standard drinks. say 4 to be on the safe side and make calculations simpler. Using the estimator in the link above, you would have a BAC of about 0.07 one hour after you start drinking. This is enough to run afoul of the current IRP legislation if you drove then or within 2 hours. By 7:00 pm, if you had nothing further to drink, your BAC would be down to about 0.001, so you would not be impaired then.